The present invention is directed to an acceleration detector for a tire of a motor vehicle, where the acceleration detector is also sensitive to the tire pressure, Sa and, thus, also functions as a pressure sensor.
In order to ensure the safety of a motor vehicle, each of its wheels is provided with a pressure sensor housed in the tire and connected by radio to a computer monitoring the state of the tires, located in the passenger compartment and indicating any abnormality. Since the sensor is inaccessible it is powered by a battery of which the life must be prolonged to the greatest possible extent. In order to do so the sensor comprises a very low power-consumption monitoring clock register which activates it only cyclically to make a measurement and emit an alarm if required.
When the vehicle is parked it is pointless to emit repeated alarms since there is no risk of accident. This sensor then operates at a slower rate with extended cycles and it only changes to the normal rate when an associated acceleration detector detects the rotation of the wheel.
A flexible blade has previously been used as an acceleration detector, mounted in a sealed Reed relay bulb housed in the tire and fixedly attached to the pressure sensor fixed to the valve. The blade established a contact controlling the change of the pressure sensor to the normal rate in the presence of the centrifugal acceleration of rotation of the wheel. In other applications, a reed bulb for detection of acceleration is similarly housed in the tire with a pressure sensor but it then serves to provide, by radio, measurements used elsewhere.
The Reed bulb, however, has the disadvantage of being relatively expensive and unable properly to withstand the shocks to which the wheels are subjected.
The present invention thus aims to provide an acceleration detector which is inexpensive and more robust.
To this end the invention relates to an acceleration detector for a tire of a motor vehicle comprising an elastically deformable membrane and, fixedly attached to the membrane, a test mass to deform it under the effect of acceleration, and an acceleration strain gauge sensitive to the deformations of the membrane under the effect of an acceleration force exerted by the test mass, characterized in that it comprises a pressure strain gauge sensitive to the pressure of the tire so that the acceleration detector also constitutes a pressure sensor.
Apart from the fact that the shocks are dampened since it is a membrane which serves to detect the acceleration, the cost of the acceleration detector is low since it also constitutes a pressure sensor.
Advantageously a pressure measuring system and an acceleration detection system are integrated, at least in part, into an integrated circuit and, preferably, the detector is formed by a component disposed in a hollow sealed housing closed by thereby, the membrane being of silicon.
In one particular embodiment, the acceleration detection system is arranged to command activation of the pressure measuring system.